They are pretty different in what they cover and how. In Instant Curriculum, it's up to you to decide what you are teaching and when. It is simply hundreds of activities for preschoolers that teach certain concepts. It's a good selection and they are well written. Has a definite "classroom" feel for the activities, though looks pretty adaptable for at-home use. You would have to decide what your child is ready for at a certain age and plan out your own schedule. It's a resource guide for the teacher. I could easily see it combined with "Peak With Books".

Flowering Baby has done the work for you. The activities are divided into five levels, one CD a level, from infancy through the fifth birthday (that aspect is sort of like Slow & Steady). There are activities for each weekday of the month, 12 months of the year (we do 4 days a week here). Your resources for each month are listed for you to make it easy, and you are given a list of suggestions what to cover each day.

So it really depends on whether you want to sit down and plan everything out, when your child is ready for each activity, or if you want most of that work done for you.